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The tuning of vertical morphology is critical and challenging for organic solar cells (OSCs). In this work, a high open-circuit voltage (V OC ) binary D18-Cl/L8-BO system is attained while maintaining the high short-circuit current (J SC ) and fill factor (FF) by employing 1,4-diiodobenzene (DIB), a volatile solid additive. It is suggested that DIB can act as a linker between donor or/and acceptor molecules, which significantly modifies the active layer morphology. The overall crystalline packing of the donor and acceptor is enhanced, and the vertical domain sizes of phase separation are significantly decreased. All these morphological changes contribute to exciton dissociation, charge transport, and collection. Therefore, the best-performing device exhibits an efficiency of 18.7% with a V OC of 0.922 V, a J SC of 26.6 mA cm -2 , and an FF of 75.6%. As far as it is known, the V OC achieved here is by far the highest among the reported OSCs with efficiencies over 17%. This work demonstrates the high competence of solid additives with two iodine atoms to tune the morphology, particularly in the vertical direction, which can become a promising direction for future optimization of OSCs., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Heterostructures built from two-dimensional (2D) materials and organic semiconductors offer a unique platform for addressing many fundamental physics and construction of functional devices by taking advantage of both the 2D materials and organic semiconductors. We report interlayer exciton emission in the near infrared range around 1.54 eV (∼805 nm) from the heterostructure of pyramidal VOPc (p-type) and transition metal dichalcogenide monolayer MoS 2 (VOPc/MoS 2 ). This contrasts the observation of photoluminescence (PL) from the SnCl 2 Pc/MoS 2 heterostructure despite both being type-II heterostructures. We attribute the exciton emission to the carrier transition from the generated interface mid-gap states of VOPc to the ground states of MoS 2 in the heterostructure system as predicted from density functional theory (DFT) calculations. Furthermore, the observed PL signal of the VOPc/MoS 2 heterostructure shows blue shift, while the PL peak of the SnCl 2 Pc/MoS 2 heterostructure shows red shift. Our finding opens up a new avenue to tune the optoelectronic properties of the van der Waals heterojunctions consisting of 2D materials and organic semiconductors for optoelectronic applications.

Coulomb interactions play a crucial role in low-dimensional semiconductor materials, e.g., 2D layered semiconductors, dictating their electronic and optical properties. However, fundamental questions remain as to whether and how Coulomb interactions affect the charge or energy flow in 2D heterostructures, which is essential for their light-electricity conversions. Herein, using ultrafast spectroscopy, we report real space coupled electron-hole dynamics in 2D heterostructures. We show in (WSe 2 /)WS 2 /MoTe 2 with a controlled energy gradient for the hole and a near flat band for electron transfer, the fate of the electron is controlled by the hole in coupled dynamics. The interfacial electron transfer from WS 2 to MoTe 2 follows the hole closely and can be facilitated or suppressed by dynamic Coulomb interaction. In parallel to the band alignment, this study reveals the critical role of Coulomb interactions on the fate of photogenerated charges in 2D heterostructures, providing experimental evidence for coupled electron-hole dynamics and a new knob for steering nanoscale charge or energy transfer process.

The heterointerface between a semiconducting metal oxide and a perovskite critically impacts on the overall performance of perovskite solar cells (PVSCs). Herein, we report a feasible yet effective strategy to suppress the interfacial reaction between nickel oxide and the perovskite via chemical passivation with self-assembled dyad molecules, which leads to the simultaneous improvement of the power conversion efficiencies (PCEs) and operational lifetimes of inverted PVSCs. As a result, inverted PVSCs consisting of simple methylammonium iodide perovskites have achieved an excellent PCE of 20.94% and decent photostability with 93% of the initial value after 600 h of 1 sun equivalent illumination. Moreover, this strategy can be readily translated into slot-die fabrication of perovskite modules, achieving a high PCE of 14.90% with an area of 19.16 cm 2 (no shade in the interconnecting area) and a geometrical fill factor of 93%. Overall, this work provides an effective strategy to stabilize the vulnerable heterointerface in PVSCs.

Nonfullerene acceptors (NFAs) are regarded as star candidates for efficient organic solar cells with power conversion efficiency (PCE) over 18%. In contrast to the rapid development of NFA materials, however, the underlying excited-state dynamics which fundamentally govern the device performance remains unclear. In this Perspective, we discuss recent advances and provide our insights on photoinduced charge transfer and combination dynamics in NFA-based organic solar cells (OSCs), including the biphasic hole-transfer process and its correlation with morphology, the role of driving force and Marcus normal region behavior on interfacial hole-transfer properties, and charge recombination energy loss by NFA triplet formation. We also discuss our understanding of how to control the charge-transfer and recombination processes by phase morphology and molecular design to improve OSC performance. Finally, we suggest a few research directions, including the interfacial charge transfer and separation mechanism, the origin of low fill factor, and complex excited-state dynamics in multicomponent OSCs.

X-ray detection, which plays an important role in medical and industrial fields, usually relies on inorganic scintillators to convert X-rays to visible photons; although several high-quantum-yield fluorescent molecules have been tested as scintillators, they are generally less efficient. High-energy radiation can ionize molecules and create secondary electrons and ions. As a result, a high fraction of triplet states is generated, which act as scintillation loss channels. Here we found that X-ray-induced triplet excitons can be exploited for emission through very rapid, thermally activated up-conversion. We report scintillators based on three thermally activated delayed fluorescence molecules with different emission bands, which showed significantly higher efficiency than conventional anthracene-based scintillators. X-ray imaging with 16.6 line pairs mm -1 resolution was also demonstrated. These results highlight the importance of efficient and prompt harvesting of triplet excitons for efficient X-ray scintillation and radiation detection., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

The bulk morphology of the active layer of organic solar cells (OSCs) is known to be crucial to the device performance. The thin film device structure breaks the symmetry into the in-plane direction and out-of-plane direction with respect to the substrate, leading to an intrinsic anisotropy in the bulk morphology. However, the characterization of out-of-plane nanomorphology within the active layer remains a grand challenge. Here, we utilized an X-ray scattering technique, Grazing-incident Transmission Small-angle X-ray Scattering (GTSAXS), to uncover this new morphology dimension. This technique was implemented on the model systems based on fullerene derivative (P3HT:PC 71 BM) and non-fullerene systems (PBDBT:ITIC, PM6:Y6), which demonstrated the successful extraction of the quantitative out-of-plane acceptor domain size of OSC systems. The detected in-plane and out-of-plane domain sizes show strong correlations with the device performance, particularly in terms of exciton dissociation and charge transfer. With the help of GTSAXS, one could obtain a more fundamental perception about the three-dimensional nanomorphology and new angles for morphology control strategies towards highly efficient photovoltaic devices., (© 2021. The Author(s).)

Because of its broad absorption and high carrier mobility, graphene has been regarded as a promising photoactive material for optoelectronics. However, its ultrashort photoexcited carrier lifetime greatly restricts the device performance. Herein, we show that by constructing a graphene/WS 2 /MoS 2 vertical heterostructure with a cascade electron-transfer pathway, the hot electrons in graphene under low-energy photoexcitation can efficiently transfer through WS 2 to MoS 2 in 180 fs, thus effectively photogating the graphene layer. Because of the spatial separation and energy barrier imposed by the WS 2 intermediate layer which retards back electron transfer, the photocarrier lifetime in graphene is significantly prolonged to ∼382.7 ps, more than 2 orders of magnitude longer than in isolated graphene and graphene/WS 2 binary heterostructure. The prolonged photocarrier lifetime in graphene leads to dramatically enhanced photocurrent generation and photoresponsivity. This study offers an exciting approach to control photocarrier lifetime in graphene for hot carrier devices with simultaneous broadband and high responsivity.

Hybrid heterostructures comprising organic and two-dimensional (2D) layered semiconductors hold great promise for light harvesting and optoelectronic applications. Among them, organic materials that exhibit singlet fission (SF) in which one singlet exciton generates two triplet excitons are particularly attractive and can potentially improve the performance of the device. However, SF-enhanced devices require that SF can compete with direct energy/charge transfer from the singlet exciton. Here, we performed ultrafast spectroscopic studies on a prototypical heterostructure consisting of tetracene (Tc) and monolayer WSe 2 . We show a type II band alignment with 16.5 ps hole transfer from photoexcited WSe 2 to tetracene and a long-lived (∼565 ps) charge separation. Importantly, we show ultrafast (∼3.4 ps) singlet exciton energy transfer from photoexcited tetracene to WSe 2 , prior to the slow SF process (>20 ps) in tetracene. This study raises the challenge and calls for the careful design of SF-enhanced 2D optoelectronic devices.

Transition metal dichalcogenide (TMD)/graphene (Gr) heterostructures constitute a key component for two-dimensional devices. The operation of TMD/Gr devices relies on interfacial charge/energy transfer processes, which remains unclear and challenging to unravel. Fortunately, the coupled spin and valley index in TMDs adds a new degree of freedom to the charges and, thus, another dimension to spectroscopy. Here, by helicity-resolved ultrafast spectroscopy, we find that photoexcitation in TMDs transfers to graphene by asynchronous charge transfer, with one type of charge transferring in the order of femtoseconds and the other in picoseconds. The rate correlates well with energy offset between TMD and graphene, regardless of compositions and charge species. Spin-polarized hole injection or long-lived polarized hole can be achieved with deliberately designed heterostructures. This study shows helicity-resolved ultrafast spectroscopy as a powerful and facile approach to reveal the fundamental and complex charge/spin dynamics in TMD-based heterostructures, paving the way toward valleytronic and optoelectronic applications., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Objective: To investigate the effect of neutrophil-to-lymphocyte ratio (NLR) on short-term prognosis in elderly patients with hip fracture., Methods: Altogether, 124 elderly patients with hip fractures who underwent surgery in our hospital were retrospectively studied, and they were divided into survival group (n=98) and death group (n=26) according to their 1-year survival. General data of both groups were collected and compared, and indicators with statistical differences in univariate analysis were further examined by logistic regression analysis. Venous blood samples were drawn from all patients 1 day after the surgery to detect and compare NLR, serum procalcitonin (PCT) and C-reactive protein (CRP) levels between both groups. ROC curve was used to analyze the clinical value of NLR in predicting the prognosis of patients. NLR cutoff value obtained by the ROC curve analysis was adopted to divide the patients into high and low ratio groups, and Kaplan-Meier (K-M) curves were used to assess the survival rate of patients in both groups., Results: There were significant differences in age, gender, marital status, medical history and American Society of Anesthesiologists (ASA) grades between both groups. Logistic regression analysis showed that advanced age (≥85 years), male gender, and higher ASA grades (III-IV) were risk factors for short-term poor prognosis in elderly patients with hip fracture. Compared with survival group, NLR, PCT and CRP levels were higher in death group. ROC curve showed that the AUC of NLR predicting patients' prognosis was 0.804 at a cutoff value of 6.939%. K-M curves showed that the overall survival was lower in high-ratio group than in low-ratio group., Conclusion: Advanced age (overall survival was lower in high-ratio group than in low-ratio group), male gender, and higher ASA grades (III-IV) were risk factors for short-term poor prognosis in elderly patients with hip rifracture. NLR has some clinical value in predicting and evaluating the prognosis of patients., Competing Interests: None., (AJTR Copyright © 2021.)

Unveiling the correlations among molecular structures, morphological characteristics, macroscopic properties and device performances is crucial for developing better photovoltaic materials and achieving higher efficiencies. To achieve this goal, a comprehensive study is performed based on four state-of-the-art non-fullerene acceptors (NFAs), which allows to systematically examine the above-mentioned correlations from different scales. It's found that extending conjugation of NFA shows positive effects on charge separation promotion and non-radiative loss reduction, while asymmetric terminals can maximize benefits from both terminals. Another molecular optimization is from alkyl chain tuning. The shortened alkyl side chain results in strengthened terminal packing and decreased π-π distance, which contribute high carrier mobility and finally the high charge collection efficiency. With the most-acquired benefits from molecular structure and macroscopic factors, PM6:BTP-S9-based organic photovoltaics (OPVs) exhibit the optimal efficiency of 17.56% (certified: 17.4%) with a high fill factor of 78.44%, representing the best among asymmetric acceptor based OPVs. This work provides insight into the structure-performance relationships, and paves the way toward high-performance OPVs via molecular design., (© 2021. The Author(s).)

Photoelectrochemical catalysis is an attractive way to provide direct hydrogen production from solar energy. However, solar conversion efficiencies are hindered by the fact that light harvesting has so far been of limited efficiency in the near-infrared region as compared to that in the visible and ultraviolet regions. Here we introduce near-infrared-active photoanodes that feature lattice-matched morphological hetero-nanostructures, a strategy that improves energy conversion efficiency by increasing light-harvesting spectral range and charge separation efficiency simultaneously. Specifically, we demonstrate a near-infrared-active morphological heterojunction comprised of BiSeTe ternary alloy nanotubes and ultrathin nanosheets. The heterojunction's hierarchical nanostructure separates charges at the lattice-matched interface of the two morphological components, preventing further carrier recombination. As a result, the photoanodes achieve an incident photon-to-current conversion efficiency of 36% at 800 nm in an electrolyte solution containing hole scavengers without a co-catalyst., (© 2021. The Author(s).)

Metal nanoclusters with distinct photophysical and photochemical properties have drawn intense research interests for their applications in optoelectronics, catalysis, and biomedicine. Herein, strong evidence is provided that light metal is capable of generating comparable optical responses of noble metal nanoclusters, but at much shorter wavelength. Air-stable, size-uniform, sub-3 nm aluminum nanocrystals are prepared with simple solution based synthetic procedures, with photoluminescence located in the ultraviolet range and short exciton lifetime. Partial modulation of the photoluminescence is achieved, indicating the key role of surface oxides. This work is envisioned to inspire new frontiers of nanocluster research with light metals., (© 2020 Wiley-VCH GmbH.)

The gas pumping method (GP) holds the potential of outperforming the antisolvent method (AS) for fabricating perovskite solar cells (PSCs) in many ways such as free of toxic solvents, improved film uniformity, and device reproducibility. Most of the highest power conversion efficiencies (PCEs) of PSCs are still achieved by AS. Successful demonstrations of inverted PSCs produced by GP as well as the corresponding mechanisms are still lacking. Herein, we fabricate highly efficient inverted PSCs by GP delivering an overall efficiency of 21.54%, on par with that of the devices by AS (21.41%), and a superior reproducibility at the optimal film thickness. Nevertheless, as the perovskite film thickness increases, the PCE of GP devices slightly dropped while the AS devices decreased significantly. We found that the AS method tends to produce horizontal grain boundaries due to the heterogeneous solvent extraction while they can be effectively suppresed by the GP method.

The donor/acceptor weight ratio is crucial for photovoltaic performance of organic solar cells (OSCs). Here, we systematically investigate the photovoltaic behaviors of PM6:Y6 solar cells with different stoichiometries. It is found that the photovoltaic performance is tolerant to PM6 contents ranging from 10 to 60 wt %. Especially an impressive efficiency over 10% has been achieved in dilute donor solar cells with 10 wt % PM6 enabled by efficient charge generation, electron/hole transport, slow charge recombination, and field-insensitive extraction. This raises the question about the origin of efficient hole transport in such dilute donor structure. By investigating hole mobilities of PM6 diluted in Y6 and insulators, we find that effective hole transport pathway is mainly through PM6 phase in PM6:Y6 blends despite with low PM6 content. The results indicate that a low fraction of polymer donors combines with near-infrared nonfullerene acceptors could achieve high photovoltaic performance, which might be a candidate for semitransparent windows.

Photo-degradation of organic semiconductors remains as an obstacle preventing their durable practice in optoelectronics. Herein, we disclose that volume-conserving photoisomerization of a unique series of acceptor-donor-acceptor (A-D-A) non-fullerene acceptors (NFAs) acts as a surrogate towards their subsequent photochemical reaction. Among A-D-A NFAs with fused, semi-fused and non-fused backbones, fully non-fused PTIC, representing one of rare existing samples, exhibits not only excellent photochemical tolerance in aerobic condition, but also efficient performance in solar cells. Along with a series of in-depth investigations, we identify that the structural confinement to inhibit photoisomerization of these unique A-D-A NFAs from molecular level to macroscopic condensed solid helps enhancing the photochemical stabilities of molecules, as well as the corresponding OSCs. Although other reasons associating with the photostabilities of molecules and devices should not excluded, we believe this work provides helpful structure-property information toward new design of stable and efficient photovoltaic molecules and solar cells.

Axially, epitaxially organizing nano-objects of distinct compositions and structures into superlattice nanowires enables full utilization of sunlight, readily engineered band structures, and tunable geometric parameters to fit carrier transport, thus holding great promise for optoelectronics and solar-to-fuel conversion. To maximize their efficiency, the general and high-precision synthesis of colloidal axial superlattice nanowires (ASLNWs) with programmable compositions and structures is the prerequisite; however, it remains challenging. Here, we report an axial encoding methodology toward the ASLNW library with precise control over their compositions, dimensions, crystal phases, interfaces, and periodicity. Using a predesigned, editable nanoparticle framework that offers the synthetic selectivity, we are able to chemically decouple adjacent sub-objects in ASLNWs and thus craft them in a controlled approach, yielding a library of distinct ASLNWs. We integrate therein plasmonic, metallic, or near-infrared-active chalcogenides, which hold great potential in solar energy conversion. Such synthetic capability enables a performance boost in target applications, as we report order-of-magnitude enhanced photocatalytic hydrogen production rates using optimized ASLNWs compared to corresponding solo objects. Furthermore, it is expected that such unique superlattice nanowires could bring out new phenomena.

The intrinsic electronic properties of donor (D) and acceptor (A) materials in coupling with morphological features dictate the output in organic solar cells (OSCs). New physical properties of intimate eutectic mixing are used in nonfullerene-acceptor-based D-A 1 -A 2 ternary blends to fine-tune the bulk heterojunction thin film morphology as well as their electronic properties. With enhanced thin film crystallinity and improved carrier transport, a significant J SC amplification is achieved due to the formation of eutectic fibrillar lamellae and reduced defects state density. Material wise, aligned cascading energy levels with much larger driving force, and suppressed recombination channels confirm efficient charge transfer and transport, enabling an improved power conversion efficiency (PCE) of 17.84%. These results reveal the importance of utilizing specific material interactions to control the crystalline habit in blended films to form a well-suited morphology in guiding superior performances, which is of high demand in the next episode of OSC fabrication toward 20% PCE., (© 2021 Wiley-VCH GmbH.)

The strong excitonic effect in monolayer transition-metal dichalcogenides (TMDs) endows them with intriguing optoelectronic properties but also short-lived population and valley polarization. Exciton dissociation by interfacial charge transfer has been shown as an effective approach to prolonging excited-state lifetimes. Herein, by ultrafast spectroscopy and building-block molecule C 60 , we investigated exciton and valley polarization dynamics in the prototypical WSe 2 /C 60 inorganic-organic hybrid. We show that excitons in WSe 2 can be dissociated through ultrafast (∼1 ps) electron transfer to C 60 , with nanosecond charge separation due to thermally activated electron diffusion in C 60 film. Because of suppressed electron-hole exchange interaction after electron transfer, hole in WSe 2 exhibits a spin/valley polarization lifetime of ∼60 ps at room temperature, more than 2 orders of magnitude longer than that in WSe 2 monolayer. This study suggests exciton dissociation as a general approach to suppress electron-hole interaction and prolong the charge/spin/valley lifetime in TMDs.

Controlling the optical response of two-dimensional (2D) layered materials is critical for their optoelectronic and photonic applications. Current transient optical modulation of 2D semiconductors is mainly based on the band filling effect, which requires internal exciton/charge occupation from photoexcitation or charge injection. However, 2D atomically thin layers exhibit a strong excitonic effect and environmental sensitivity, offering exciting opportunities to engineer their optical properties through an external dielectric or electronic environment. Here, using femtosecond transient absorption spectroscopy as a tool and transition-metal dichalcogenide (TMD) van der Waals heterostructures with type I band alignment, we show the transient absorption modulation of the TMD layer by excitons at ultimate proximity without direct photoexcitation or exciton/charge occupation. Further layer-dependent study indicates the presence of excitons reduces the exciton oscillator strength in adjacent layers through the electric field effect because of environmental sensitivity and proximity of 2D materials. This result demonstrates the transient optical modulation with decoupled light absorption and modulation components and suggests an alternative approach to control the optical response of 2D materials for optoelectronic and photonic applications.

Two-dimensional (2D) lead halide perovskites with distinct excitonic feature have shown exciting potential for optoelectronic applications. Compared to their three-dimensional counterparts with large polaron character, how the interplay between long- and short- range exciton-phonon interaction due to polar and soft lattice define the excitons in 2D perovskites is yet to be revealed. Here, we seek to understand the nature of excitons in 2D CsPbBr 3 perovskites by static and time-resolved spectroscopy which is further rationalized with Urbach-Martienssen rule. We show quantitatively an intermediate exciton-phonon coupling in 2D CsPbBr 3 where exciton polarons are momentarily self-trapped by lattice vibrations. The 0.25 ps ultrafast interconversion between free and self-trapped exciton polaron with a barrier of ~ 34 meV gives rise to intrinsic asymmetric photoluminescence with a low energy tail at room temperature. This study reveals a complex and dynamic picture of exciton polarons in 2D perovskites and emphasizes the importance to regulate exciton-phonon coupling.

The chemical structure of donors and acceptors limit the power conversion efficiencies achievable with active layers of binary donor-acceptor mixtures. Here, using quaternary blends, double cascading energy level alignment in bulk heterojunction organic photovoltaic active layers are realized, enabling efficient carrier splitting and transport. Numerous avenues to optimize light absorption, carrier transport, and charge-transfer state energy levels are opened by the chemical constitution of the components. Record-breaking PCEs of 18.07% are achieved where, by electronic structure and morphology optimization, simultaneous improvements of the open-circuit voltage, short-circuit current and fill factor occur. The donor and acceptor chemical structures afford control over electronic structure and charge-transfer state energy levels, enabling manipulation of hole-transfer rates, carrier transport, and non-radiative recombination losses.

Among light-based free-space communication platforms, mid-infrared (MIR) light pertains to important applications in biomedical engineering, environmental monitoring, and remote sensing systems. Integrating MIR generation and reception in a network using two identical devices is vital for the miniaturization and simplification of MIR communications. However, conventional MIR emitters and receivers are not bidirectional due to intrinsic limitations of low performance and often require cryogenic cooling. Here, we demonstrate that macroscopic graphene fibres (GFs) assembled from weakly-coupled graphene layers allow room-temperature MIR detection and emission with megahertz modulation frequencies due to the persistence of photo-thermoelectric effect in millimeter-length and the ability to rapidly modulate gray-body radiation. Based on the dual-functionality of GFs, we set up a system that conducts bidirectional data transmission by switching modes between two identical GFs. The room-temperature operation of our systems and the potential to produce GFs on industrial textile-scale offer opportunities for simplified and wearable optical communications.

Quantum-dot light-emitting diodes (QLEDs) promise a new generation of high-performance, large-area, and cost-effective electroluminescent devices for both display and solid-state lighting technologies. However, a positive ageing process is generally required to improve device performance for state-of-the-art QLEDs. Here, it is revealed that the in situ reactions induced by organic acids in the commonly used encapsulation acrylic resin lead to positive ageing and, most importantly, the progression of in situ reactions inevitably results in negative ageing, i.e., deterioration of device performance after long-term shelf storage. In-depth mechanism studies focusing on the correlations between the in situ chemical reactions and the shelf-ageing behaviors of QLEDs inspire the design of an electron-transporting bilayer, which delivers both improved electrical conductivity and suppressed interfacial exciton quenching. This material innovation enables red QLEDs exhibiting neglectable changes of external quantum efficiency (>20.0%) and ultralong operational lifetime (T 95 : 5500 h at 1000 nits) after storage for 180 days. This work provides design principles for oxide electron-transporting layers to realize shelf-stable and high-operational-performance QLEDs, representing a new starting point for both fundamental studies and practical applications., (© 2020 Wiley-VCH GmbH.)

Two-dimensional lead halide perovskites with confined excitons have shown exciting potentials in optoelectronic applications. It is intriguing but unclear how the soft and polar lattice redefines excitons in layered perovskites. Here, we reveal the intrinsic exciton properties by investigating exciton spin dynamics, which provides a sensitive probe to exciton coulomb interactions. Compared to transition metal dichalcogenides with comparable exciton binding energy, we observe orders of magnitude smaller exciton-exciton interaction and, counterintuitively, longer exciton spin lifetime at higher temperature. The anomalous spin dynamics implies that excitons exist as exciton polarons with substantially weakened inter- and intra-excitonic interactions by dynamic polaronic screening. The combination of strong light matter interaction from reduced dielectric screening and weakened inter-/intra-exciton interaction from dynamic polaronic screening explains their exceptional performance and provides new rules for quantum-confined optoelectronic and spintronic systems., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Herein we develop a new pillar[5]arene-mediated supramolecular polymerization strategy to control the assembly of dyes 4,7-di-2-thienyl-2,1,3-benzothiadiazole and 4,7-di-2-thienyl-2,1,3-benzoselenadiazole in the solid state. The resulting supramolecular polymeric structures drive the dye aggregates in the solid state from parallel alignments to highly ordered "head-to-tail" structures, which effectively suppresses excimer formation and thus aggregation-caused quenching effects and enhances the solid-state emission efficiency by almost 1 order of magnitude. This, together with two-photon excited emission, endows these solid-state polymers with exciting potential in optoelectronic, photonic, and bioimaging applications.

2D perovskite solar cells with high stability and high efficiency have attracted significant attention. A systematical static and dynamic structure investigation is carried out to show the details of 2D morphology evolution. A dual additive approach is used, where the synergy between an alkali metal cation and a polar solvent leads to high-quality 2D perovskite films with sandwich-type structures and vertical phase segregation. Such novel structure can induce high-quality 2D slab growth and reduce internal and surface defects, resulting in a high device efficiency of 16.48% with enhanced continuous illumination stability and improved moisture (55-60%) and thermal (85 °C) tolerances. Transient absorption spectra reveal the carrier migration from low n to high n species with different kinetics. An [PbI 6 ] 4- octagon coalescence transformation mechanism coupled with metal and organic cations wrapped is proposed. By solvent vapor annealing, a recrystallization and reorientation of the 2D perovskite slabs occurs to form an ideal structure with improved device performance and stability., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Clean energy production and saving play vital impacts on the sustainability of the global community. Herein, high-performance semitransparent organic solar cells (ST-OSCs) with excellent features of power generation, being see-through, and infrared reflection of heat dissipation, with promising perspectives for building-integrated photovoltaics (BIPVs) are reported. To simultaneously improve average visible transmittance (AVT) and power conversion efficiency (PCE), formally in a trade-off relationship, of ST-OSCs, new ternary blends with alloy-like near-infrared (NIR) acceptors are employed, which are effective to improve device efficiency while maintaining visible absorption unchanged, resulting in PCEs of 16.8% for opaque devices and 13.1% for semitransparent OSCs (AVT of 22.4% and infrared photon radiation rejection (IRR) of 77%). Further, multifunctional ST-OSCs are realized via introducing simple, yet effective photonic reflectors, together with optical simulation, leading to not only perfect fitting of the visible transmittance peak (555 nm) to the photopic response of the human eye but also an excellent IRR of 90% (780-2500 nm), along with 23% AVT and over 12% PCE. This is thought to be the best-performing multifunctional ST-OSC with promising prospects as BIPVs in terms of power generation, heat dissipation, and being see-through., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

X-rays are widely used in probing inside information nondestructively, enabling broad applications in the medical radiography and electronic industries. X-ray imaging based on emerging lead halide perovskite scintillators has received extensive attention recently. However, the strong self-absorption, relatively low light yield and lead toxicity of these perovskites restrict their practical applications. Here, we report a series of nontoxic double-perovskite scintillators of Cs 2 Ag 0.6 Na 0.4 In 1-y Bi y Cl 6 . By controlling the content of the heavy atom Bi 3+ , the X-ray absorption coefficient, radiative emission efficiency, light yield and light decay were manipulated to maximise the scintillator performance. A light yield of up to 39,000 ± 7000 photons/MeV for Cs 2 Ag 0.6 Na 0.4 In 0.85 Bi 0.15 Cl 6 was obtained, which is much higher than that for the previously reported lead halide perovskite colloidal CsPbBr 3 (21,000 photons/MeV). The large Stokes shift between the radioluminescence (RL) and absorption spectra benefiting from self-trapped excitons (STEs) led to a negligible self-absorption effect. Given the high light output and fast light decay of this scintillator, static X-ray imaging was attained under an extremely low dose of ∼1 μGy air , and dynamic X-ray imaging of finger bending without a ghosting effect was demonstrated under a low-dose rate of 47.2 μGy air  s -1 . After thermal treatment at 85 °C for 50 h followed by X-ray irradiation for 50 h in ambient air, the scintillator performance in terms of the RL intensity and X-ray image quality remained almost unchanged. Our results shed light on exploring highly competitive scintillators beyond the scope of lead halide perovskites, not only for avoiding toxicity but also for better performance., Competing Interests: Conflict of interestThe authors declare that they have no conflicts of interest., (© The Author(s) 2020.)

Non-noble metal plasmonic materials, e.g. doped semiconductor nanocrystals, compared to their noble metal counterparts, have shown unique advantages, including broadly tunable plasmon frequency (from visible to infrared) and rich surface chemistry. However, the fate and harvesting of hot electrons from these non-noble metal plasmons have been much less explored. Here we report plasmon driven hot electron generation and transfer from plasmonic metal oxide nanocrystals to surface adsorbed molecules by ultrafast transient absorption spectroscopy. We show unambiguously that under infrared light excitation, hot electron transfers in ultrafast timescale (<50 fs) with an efficiency of 1.4%. The excitation wavelength and fluence dependent study indicates that hot electron transfers right after Landau damping before electron thermalization. We revealed the efficiency-limiting factors and provided improvement strategies. This study paves the way for designing efficient infrared light absorption and photochemical conversion applications based on non-noble metal plasmonic materials.

Deciphering the complicated excited-state process is critical for the development of luminescent materials with controllable emissions in different applications. Here we report the emergence of a photo-induced structural distortion accompanied by an electron redistribution in a series of gold nanoclusters. Such unexpected slow process of excited-state transformation results in near-infrared dual emission with extended photoluminescent lifetime. We demonstrate that this dual emission exhibits highly sensitive and ratiometric response to solvent polarity, viscosity, temperature and pressure. Thus, a versatile luminescent nano-sensor for multiple environmental parameters is developed based on this strategy. Furthermore, we fully unravel the atomic-scale structural origin of this unexpected excited-state transformation, and demonstrate control over the transition dynamics by tailoring the bi-tetrahedral core structures of gold nanoclusters. Overall, this work provides a substantial advance in the excited-state physical chemistry of luminescent nanoclusters and a general strategy for the rational design of next-generation nano-probes, sensors and switches.

Low energy loss and efficient charge separation under small driving forces are the prerequisites for realizing high power conversion efficiency (PCE) in organic photovoltaics (OPVs). Here, a new molecular design of nonfullerene acceptors (NFAs) is proposed to address above two issues simultaneously by introducing asymmetric terminals. Two NFAs, BTP-S1 and BTP-S2, are constructed by introducing halogenated indandione (A 1 ) and 3-dicyanomethylene-1-indanone (A 2 ) as two different conjugated terminals on the central fused core (D), wherein they share the same backbone as well-known NFA Y6, but at different terminals. Such asymmetric NFAs with A 1 -D-A 2 structure exhibit superior photovoltaic properties when blended with polymer donor PM6. Energy loss analysis reveals that asymmetric molecule BTP-S2 with six chlorine atoms attached at the terminals enables the corresponding devices to give an outstanding electroluminescence quantum efficiency of 2.3 × 10 -2 %, one order of magnitude higher than devices based on symmetric Y6 (4.4 × 10 -3 %), thus significantly lowering the nonradiative loss and energy loss of the corresponding devices. Besides, asymmetric BTP-S1 and BTP-S2 with multiple halogen atoms at the terminals exhibit fast hole transfer to the donor PM6. As a result, OPVs based on the PM6:BTP-S2 blend realize a PCE of 16.37%, higher than that (15.79%) of PM6:Y6-based OPVs. A further optimization of the ternary blend (PM6:Y6:BTP-S2) results in a best PCE of 17.43%, which is among the highest efficiencies for single-junction OPVs. This work provides an effective approach to simultaneously lower the energy loss and promote the charge separation of OPVs by molecular design strategy., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The singlet fission (SF) process converts one high-energy singlet exciton to two low-energy triplet excitons after absorbing one photon. Organic photovoltaic devices based on the SF process have shown great potential in solar energy conversion to exceed Shockley-Queisser limit. The key to SF photovoltaic devices requires efficient electron transfer (ET) from triplet exciton after SF, which is yet to be thoroughly investigated. Here, we performed thorough photophysical studies in 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/C 60 heterostructures using TIPS-pentacene microsize single crystal as a well-defined model system. We show the SF process in TIPS-pentacene single crystal occurs by a two-step process, with triplet pair intermediates forming in 75 fs and then dissociating to non-interacting triplets in 1.6 ps. The SF process in single crystal is comparable to that in polycrystalline film. Importantly, we observe a considerable fraction of singlet excitons is quenched by ultrafast (<75 fs) interfacial ET prior to fission and no ET from triplet excitons in 1.5 ns time window. We confirm that the absence of ET is not limited by exciton diffusion but due to very slow (≫1.5 ns) interfacial ET from triplet exciton. The observations contradict expected singlet and triplet ET behaviors based on a simple two-state Marcus ET model and suggest long-range interfacial ET from delocalized photoexcitation. The ultrafast ET from singlet exciton before SF and slow ET from triplet exciton call for reconsideration and careful design of efficient SF photovoltaic devices.

Nonfullerene acceptors (NFAs) have attracted great attention in high-efficiency organic solar cells (OSCs). While the effect of molecular properties including structures and energetics on charge transfer has been extensively investigated, the effect of macroscopic-phase properties is yet to be revealed. Here we have performed a correlation study of the nanoscale-phase morphology on the photoexcited hole transfer (HT) process and photovoltaic performance by combining ultrafast spectroscopy with high temporal resolution and photo-induced force microscopy (PiFM) with high spatial and chemical resolution. In PM6/IT-4F, we observe biphasic HT behavior with a minor ultrafast (<100 fs) interfacial process and a major diffusion-mediated HT process until ∼100 ps, which depends strongly on phase segregation. Because of the interplay between charge transfer and transport, a compromised domain size of 20-30 nm for NFAs shows the best performance. This study highlights the critical role of phase morphology in high-efficiency OSCs.

It is very important to fine-tune the nanoscale morphology of donor:acceptor blend active layers for improving the photovoltaic performance of all-small-molecule organic solar cells (SM-OSCs). In this work, two new small molecule donor materials are synthesized with different substituents on their thiophene conjugated side chains, including SM1-S with alkylthio and SM1-F with fluorine and alkyl substituents, and the previously reported donor molecule SM1 with an alkyl substituent, for investigating the effect of different conjugated side chains on the molecular aggregation and the photophysical, and photovoltaic properties of the donor molecules. As a result, an SM1-F-based SM-OSC with Y6 as the acceptor, and with thermal annealing (TA) at 120 °C for 10 min, demonstrates the highest power conversion efficiency value of 14.07%, which is one of the best values for SM-OSCs reported so far. Besides, these results also reveal that different side chains of the small molecules can distinctly influence the crystallinity characteristics and aggregation features, and TA treatment can effectively fine-tune the phase separation to form suitable donor-acceptor interpenetrating networks, which is beneficial for exciton dissociation and charge transportation, leading to highly efficient photovoltaic performance., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Two-dimensional (2D) materials and heterostructures with strong excitonic effect and spin/valley properties have emerged as an exciting platform for optoelectronic and spin/valleytronic applications. There, precise control of the exciton transformation process (including intralayer to interlayer exciton transition and recombination) and valley polarization process via structural tuning is crucial but remains largely unexplored. Here, using hexagonal boron nitride (BN) as an intermediate layer, we show the fine-tuning of exciton and valley dynamics in 2D heterostructures with atomic precision. Both interfacial electron and hole transfer rates decrease exponentially with increasing BN thickness, which can be well-described with quantum tunneling model. The increased spatial separation with BN intercalation weakens the electron-hole Coulomb interaction and significantly prolongs the interlayer exciton population and valley polarization lifetimes in van der Waals (vdW) heterostructures. For example, WSe 2 /WS 2 heterostructures with monolayer BN intercalation exhibit a hole valley polarization lifetime of ∼60 ps at room temperature, which is approximately threefold and 3 orders of magnitude longer than that in WSe 2 /WS 2 heterobilayer without BN and WSe 2 monolayer, respectively. Considering a large family of layered materials, this study suggests a general approach to tailor and optimize exciton and valley properties in vdW heterostructures with atomic precision.

0D-2D mixed-dimensional hybrid structures, which combine tunable optical properties of 0D quantum dots (QDs) and high transport mobilities of 2D layered materials, have shown great potential in optoelectronic applications. Understanding charge transfer dynamics at the 0D-2D interface is essential but still lacking. Here, using PbS QD/WSe 2 system, by simply controlling PbS QD size, we show a tunable hole transfer (HT) rate by more than 4 orders of magnitude (from ∼1 ns to <100 fs) and, interestingly, transition from the weak to strong coupling regime due to quantum confinement effect. In contrast to reported layer-dependent energy transfer dynamics, we observe a robust HT rate against WSe 2 layer number, which can be ascribed to a subtle change of WSe 2 valence band structure with layer number. Our results are important to not only fundamental understanding of charge transfer behavior at nanoscale low-dimensional interface but also help design next-generation mixed-dimensional optoelectronic devices.

Although the unique hot carrier characteristics in graphene suggest a new paradigm for hot carrier-based energy harvesting, the reported efficiencies with conventional photothermoelectric and photothermionic emission pathways are quite low because of inevitable hot carrier thermalization and cooling loss. Here, we proposed and demonstrated the possibility of efficiently extracting hot electrons from graphene after carrier intraband scattering but before electron-hole interband thermalization, a new regime that has never been reached before. Using various layered semiconductors as model electron-accepting components, we generally observe ultrafast injection of energetic hot electrons from graphene over a very broad photon energy range (visible to mid-infrared). The injection quantum yield reaches as high as ~50%, depending on excitation energy but remarkably, not on fluence, in notable contrast with conventional pathways with nonlinear behavior. Hot electron harvesting in this regime prevails over energy and carrier loss and closely resembles the concept of hot carrier solar cell., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

By using click chemistry, a hexacationic cage was synthesized. The cage contains two triscationic π-electron-deficient trispyridiniumtriazine (TPZ 3+ ) platforms that are bridged in a face-to-face manner by three ethylene-triazole-ethylene linkers. A diversity of π-electron-rich guests can be recognized within the pocket of the cage, driven by host-guest π-π interactions. The cage cavity acts as a protecting group, preventing an anthracene guest from undergoing Diels-Alder reaction. Under ultraviolet (UV) light, the pyridinium C─N bonds in TPZ 3+ platforms are polarized and weakened, resulting in the occurrence of cage decomposition via β-elimination. Guest recognition could help to prevent this UV-stimulated cage decomposition by suppressing the excitation of the TPZ 3+ units., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Heavily self-doped semiconductors can be designed to be used in advanced photonics due to both fabrication and functional advantages. Ultrafast response, strong optical nonlinearity, broadband wavelength range, and accessibility of integration are major challenges for ultrafast all-optical photonics to operate in the infrared wavelength range. Here, solution-processed Cu 1.8 Se semiconductor nanocrystals (NCs) demonstrate an ultrafast response (about 360-520 fs), strong optical nonlinearity (as large as -1.4 × 10 3 cm GW -1 ), and broadband (from 800 to 3000 nm) nonlinear optical absorption in the near-infrared and mid-infrared wavelength ranges. The ultrafast response and larger optical nonlinearity may be triggered by the plasma ground-state bleaching in the strong surface electromagnetic filed. Stable Q-switched lasers in Er-doped fiber laser, Tm-doped fiber laser, and Ho/Pr-codoped ZBLAN fiber laser are operated, respectively. These findings indicate that Cu 1.8 Se NCs are prospective nonlinear materials for ultrafast response and broadband pulse laser.

In this work, a novel heterostructure consisting of different lattice structures with zincblende ZnTe and rock-salt PbTe is proposed. The PbTe/ZnTe heterostructures are grown by molecular beam epitaxy. Type-I band alignment at the PbTe/ZnTe heterointerface is revealed by X-ray photoelectron spectroscopy. The interface of the heterostructure exhibits exotic electrical properties. The novel heterostructure is then implemented to develop high-performance mid-infrared photodetectors which demonstrate pronounced responsivity, swift response speed, and high detectivity. The new photodetectors utilize the lateral photovoltaic effect which facilitates the understanding of the novel PbTe/ZnTe heterostructures.

For state-of-the-art organic solar cells (OSCs) consisting of a large-bandgap polymer donor and a near-infrared (NIR) molecular acceptor, the control of the HOMO offset is the key to simultaneously achieve small energy loss (E loss ) and high photocurrent. However, the relationship between HOMO offsets and the efficiency for hole separation is quite elusive so far, which requires a comprehensive understanding on how small the driving force can effectively perform the charge separation while obtaining a high photovoltage to ensure high OSC performance. By designing a new family of ZITI-X NIR acceptors (X = S, C, N) with a high structural similarity and matching them with polymer donor J71 forming reduced HOMO offsets, we systematically investigated and established the relationship among the photovoltaic performance, energy loss, and hole-transfer kinetics. We achieved the highest PCE avg s of 14.05 ± 0.21% in a ternary system (J71:ZITI-C:ZITI-N) that best optimize the balance between driving force and energy loss., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

Because of their earth-abundant, low-cost, and environmentally benign characteristics, two-dimensional (2D) group IV metal chalcogenides (e.g., SnSe 2 ) with layered structures have shown great potential in optoelectronic, photovoltaic, and thermoelectric applications. However, the intrinsic motion of excited carriers and their coupling with lattice photons, which fundamentally dictates device operation and optimization, remain yet to be unraveled. Herein, we directly follow the ultrafast carrier and photon dynamics of colloidal SnSe 2 nanosheets in real time using ultrafast transient absorption spectroscopy. We show ∼0.3 ps intervalley relaxation process of photoexcited energetic carriers and ∼3 ps carrier defect trapping process with a long-lived trapped carrier (∼1 ns), highlighting the importance of trapped carriers in optoelectronic devices. In addition, ultrashort laser pulse impulsively drives coherent out-of-plane lattice vibration in SnSe 2 , indicating strong electron-phonon coupling in SnSe 2 . This strong electron-phonon coupling could impose a fundamental limit on SnSe 2 photovoltaic devices but benefit its thermoelectric applications.

Chemical systems with external control capability and self-recoverability are promising since they can avoid additional chemical or energy imposition during the working process. However, it remains challenging to employ such a nonequilibrium method for the engineering of optoelectronic function and for visualization. Here, we report a functional molecule that can undergo intense conformational regulation upon photoexcitation. It enables a dynamical change in hydrophobicity and a follow-up molecular aggregation in aqueous media, accordingly leading to an aggregation-induced phosphorescence (AIP) behavior. This successive performance is self-recoverable, allowing a rapid (second-scale cycle) and long-standing (>10 3 cycles) flicker ability under rhythmical control of the AIP. Compared with traditional bidirectional manipulations, such monodirectional photocontrol with spontaneous reset profoundly enhances the operability while mostly avoiding possible side reactions and fatigue accumulation. Furthermore, this material can serve as a type of luminescent probe for dynamically strengthening visualization in bioimaging., Competing Interests: The authors declare no conflict of interest.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have shown great potential in ultrathin and flexible optoelectronic and photonics devices. Besides emissive bright excitons, they also possess rich non-emissive dark excitons including momentum-forbidden indirect excitons and spin-forbidden triplet-like excitons, which could be dominant species under optical or electrical excitation in 2D optoelectronic and photonic devices. Efficient harvesting of both bright and dark excitons from TMDs and understanding the exciton-transfer mechanism consequently are not only of fundamental interest but also a technological challenge. Here, by combining steady-state photoluminescence spectroscopy and ultrafast transient reflectance spectroscopy, we show efficient exciton harvesting by ultrafast energy transfer in WSe 2 /MoTe 2 van der Waals heterostructures, leading to the photoluminescence enhancement of MoTe 2 . The energy transfer occurs with near-unity yield and in an ultrafast (∼200 fs) manner for both bright and dark excitons, suggesting a dominant Dexter-type energy-transfer process consisting of simultaneous transfer of both electron and hole in van der Waals coupled 2D layers at ultimate proximity. This result is beyond the conventional dipole-dipole coupling mechanism typically assumed at 2D interfaces and offers a path to high speed and enhanced light harvesting and emission applications based on 2D heterostructures.

Herein, we investigated a series of fullerene-free organic solar cells (OSCs) based on six different donor:acceptor (D:A) blends with varied highest occupied molecular orbital (HOMO) offsets from -0.05 to 0.21 eV. First, to verify the energetic compatibility of a specific D:A pair, especially for HOMO offsets, we established a simple method to estimate the hole transfer tendencies between D and A by using bilayer hole-only devices. It reveals that the asymmetrical diode effect of the bilayer hole-only devices can correlate with the FF and J sc of the relevant OSCs. Second, to find out whether HOMO offset is the main restriction of hole transfer, we measured transient absorption spectra and examined the hole transfer behavior in the blends, revealing that the occurrence of hole transfer is independent of the HOMO offsets and ultrafast in the time scale of ≤4.6 ps for those blends with ≥0 eV HOMO offsets. In contrast, a negative HOMO offset can significantly slow down the hole transfer with a half-time of ∼400 ps. Furthermore, we compare the device parameters under varied light intensities and discover that the bimolecular recombination should be one of the main restrictions for high device performance. Surprisingly, small HOMO offsets of 0 and 0.06 eV can also enable high PCEs of 10.42% and 11.75% for blend 2 (PTQ10:HC-PCIC) and blend 3 (PBDB-TF:HC-PCIC), respectively. Overall, our work demonstrates not only the validity of high-performance OSCs operating at the near zero HOMO offsets but also the charge dynamic insights of these blends, which will help gain understanding on the further improvement of OSCs.

Hybrid lead halide perovskites exhibit carrier properties that resemble those of pristine nonpolar semiconductors despite static and dynamic disorder, but how carriers are protected from efficient scattering with charged defects and optical phonons is unknown. Here, we reveal the carrier protection mechanism by comparing three single-crystal lead bromide perovskites: CH 3 NH 3 PbBr 3 , CH(NH 2 ) 2 PbBr 3 , and CsPbBr 3 We observed hot fluorescence emission from energetic carriers with ~10 2 -picosecond lifetimes in CH 3 NH 3 PbBr 3 or CH(NH 2 ) 2 PbBr 3 , but not in CsPbBr 3 The hot fluorescence is correlated with liquid-like molecular reorientational motions, suggesting that dynamic screening protects energetic carriers via solvation or large polaron formation on time scales competitive with that of ultrafast cooling. Similar protections likely exist for band-edge carriers. The long-lived energetic carriers may enable hot-carrier solar cells with efficiencies exceeding the Shockley-Queisser limit., (Copyright © 2016, American Association for the Advancement of Science.)

Type I core/shell quantum dots (QDs) have been shown to improve the stability and conversion efficiency of QD-sensitized solar cells compared to core only QDs. To understand how the shell thickness affects the solar cell performance, its effects on interfacial charge separation and recombination kinetics are investigated. These kinetics are measured in CdSe/ZnS type I core/shell QDs adsorbed with anthroquinone molecules (as electron acceptor) by time-resolved transient absorption spectroscopy. We show that the charge separation and recombination rates decrease exponentially with the shell thickness (d), k(d) = k(0)e(-βd), with exponential decay factors β of 0.35 ± 0.03 per Å and 0.91 ± 0.14 per Å, respectively. Model calculations show that these trends can be attributed to the exponential decrease of the 1S electron and hole densities at the QD surface with the shell thickness. The much steeper decrease in charge recombination rate results from a larger hole effective mass (than electron) in the ZnS shell. This finding suggests possible ways of optimizing the charge separation yield and lifetime by controlling the thickness and nature of the shell materials.

Objective: To study the molecular typing of 78 strains of Vibrio parahaemolyticus isolated from Guangdong by MPN method with pulsed-field gel electrophoresis (PFGE) and automated ribotyping (RP)., Methods: DNAs from all strains were digested by EcoR I for ribotyping and digested by Sfi I and Not I for PFGE. The band patterns of PFGE and RP were clustering adn analyzed by BioNumerics software., Results: There were 64, 68 and 71 kinds of band patterns of each Vibrio parahaemolyticus strain digested by restriction endonuclease EcoR I, Sfi I and Not I respectively. The band patterns of some strains from the same sample are completely identical, but the band patterns of most strains are different and are divided into different groups., Conclusion: PFGE is a rapid, robust, and reproducible genotyping technique, more discriminative than automated ribotyping. Choosing more isolates from MPN method for suspected food samples should be considered in tracing the phylogenetic relationship of strains.